The invention relates in general to a protective helmet and in particular to a new and useful protective helmet having interengageable inner and outer portions.
A protective helmet according to the invention is appropriate for situations where an exact fixation of the helmet with regard to the head of the user is required.
German Patent No. 29 01 088 describes an integral protective helmet whose outer shell can be split, and so can its inner shell, which is fixedly connected to the outer shell halves. This integral protective helmet encloses the head, the chin area and the cheeks. The custom-formable, inflatable inner part serves to fix the head inside the helmet. The helmet can be pulled off the head of the wearer once the valve of the inflatable inner part is opened or the helmet is split. The contact surfaces of the shells of the helmet are formed with a slot and feather interconnection, the shell halves being kept together by means of suitably disconnectable means in the shape of a strap around the two shell halves once the halves are joined.
It is disadvantageous in this known helmet that its mechanical stability is inferior compared to a helmet with a one-piece shell and that it does not fit the head without play as the inflatable insert can be fitted to the shape of the head only to a limited extent. An insert which is blown up too strongly also decreases the comfort. As the inner shell does not enclose the chin region from below, a rotation of the helmet in the direction of the body axis is possible.
Another known helmet for pilots comprises a hard outer shell and an inner shell which can be split into several parts custom fitted for the wearer and fixed inside the outer shell. The splitting is required to allow for an inserting and fixation of the shell halves inside the outer shell one by one. The inner shell can be glued in or be fixed by means of velcro-tape or such like.
The inner shell includes foam parts and encloses the hairy part of the head from the forehead down to the neck. Both the outer and the inner shell are slipped onto the head of the user at the same time. For this reason undercuts in the area of the inner contour of the inner shell are not possible. For reasons of fit the entering contour in the area of the neck opening is closed slightly conical in the described embodiment so that the helmet lies close in the cheek area. Such helmets are offered by several manufacturers, such as Gentex, type HGU-55/G, Foam Custom Fit Version. It is disadvantageous that considerable force has to be exerted during the putting on and taking off of the helmet due to the conical contour of the entrance, thus decreasing the overall comfort.
If additional instruments, such as optical target acquisition, are used, which are attached to the outer shell of the helmet, often the total play between head and helmet becomes too large as the inner shell encloses only a part of the head. In addition, acceleration forces and moments exerting force from outside on the helmet can only be received in those directions where a rotation of the head with regard to the helmet is not possible due to the geometrical design of the inner contour.
The outer and the inner shell of the helmet form a unit, the inner shell being custom fitted to the head of the individual wearer. Therefore each helmet is assigned to a single wearer. If the devices attached to the outer helmet shell are to be used by another pilot, the helmet has to be refitted or several complete special helmets have to be provided for every pilot. These solutions are time-consuming and expensive.